KR101747307B1 - Apparatus for encoding/decoding multichannel signal and method thereof - Google Patents

Abstract

An apparatus for encoding / decoding a multi-channel signal is disclosed. A multi-channel signal encoding apparatus processes a phase parameter for phase information between a plurality of channels constituting a multi-channel signal in consideration of characteristics of a multi-channel signal. And generates an encoded bit stream for the multi-channel signal using the processed phase parameter and the mono signal extracted from the multi-channel signal.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an apparatus and a method for encoding / decoding multi-channel signals,

Embodiments of the present invention relate to an apparatus and method for encoding / decoding a multi-channel signal, and more particularly to an apparatus and method for encoding / decoding a multi-channel signal using phase information.

A method used to encode a stereo signal is parametric stereo (PS) technology. The parametric stereo technique generates a mono signal by downmixing an input stereo signal, extracts a stereo parameter indicating side information on the stereo signal, codes the generated mono signal and the extracted stereo parameter, And encodes the signal.

In this case, the stereo parameters used include Inter-channel Intensity Difference (IID) or Channel Level Differences (CLD) indicating intensity differences according to energy levels of at least two channel signals included in the stereo signal, at least two channels (Inter-channel Coherence or Inter-channel Correlation) indicating the correlation between two channel signals according to the similarity of the waveform of the signal, an inter-channel coherence or inter-channel correlation And OPD (Overall Phase Difference) indicating how the phase difference between at least two channel signals included in the stereo signal is distributed between the two channels based on the mono signal.

 An apparatus for encoding a multi-channel signal according to an embodiment of the present invention includes a parameter extraction unit that extracts a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting a multi-channel signal, A parameter coding unit for coding the plurality of parameters including the modified phase parameter, a mono signal coding unit for coding a mono signal obtained by downmixing the multi-channel signal, And a bitstream generator for generating an encoded bitstream for the multi-channel signal using the plurality of parameters and the encoded mono signal.

In this case, the plurality of parameters include energy level difference (CLD) between the plurality of channels, and when the CLD is 0 and the IPD is 180, the parameter modifying unit adjusts the IPD to 0 degrees Modify it.

According to another aspect of the present invention, there is provided an apparatus for encoding a multi-channel signal, the apparatus comprising: a parameter extraction unit that extracts a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting a multi-channel signal; And a parameter encoding unit which encodes the plurality of parameters including the phase parameter when encoding of the phase parameter is determined.

According to another aspect of the present invention, there is provided an apparatus for encoding a multi-channel signal, the apparatus comprising: a parameter extraction unit that extracts a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting a multi-channel signal; A parameter encoding unit for encoding a plurality of quantized parameters, a mono signal encoding unit for encoding a mono signal obtained by downmixing the multi-channel signal, and a multi-channel signal encoding unit for encoding the multi-channel signal using the plurality of encoded parameters and the encoded mono signal. The parameter encoding unit determines a quantization level of the phase parameter based on continuity of phase information between a plurality of frames included in the multi-channel signal.

Also, an apparatus for decoding a multi-channel signal according to an embodiment of the present invention includes a mono signal decoding unit for decoding a mono signal, which is a downmix signal of the multi-channel signal, from a bitstream of a multi- A parameter decoding unit for restoring a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting a multi-channel signal; a parameter decoding unit for decoding a parameter (OPD) related to a phase difference between the restored monaural signal and the multi- A parameter estimator for estimating an overall phase difference, a parameter modifying unit for modifying the estimated OPD, and an upmixing unit for upmixing the mono signal using the restored at least one parameter and the modified OPD do.

At this time, the plurality of parameters include CLD and IPD, and the parameter modifying unit can modify the OPD based on the CLD and the IPD.

Also, an upmixing unit for upmixing the mono signal using a parameter correcting unit for correcting a parameter related to a phase difference between a mono signal and a multi-channel signal, which is a downmix signal of the multi-channel signal, Is provided.

A parameter extracting unit for extracting a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting a multi-channel signal; a parameter correcting unit for correcting a phase parameter relating to phase information between a plurality of channels among the plurality of parameters; A downmixing unit for downmixing a multi-channel signal to generate a mono signal, and a bitstream generator for encoding the plurality of parameters and the generated mono signal except for the modified phase parameter to generate a bitstream / RTI >

An apparatus and method for encoding / decoding a multi-channel signal according to an embodiment of the present invention can reduce the amount of data required for data transmission.

An apparatus and method for encoding / decoding a multi-channel signal according to an embodiment of the present invention can provide a multi-channel audio signal with improved sound quality.

1 is a block diagram showing a detailed configuration of an apparatus for encoding a multi-channel signal according to an embodiment of the present invention.
Fig. 2 is a conceptual diagram for explaining a change in a phase parameter in successive frames included in a stereo signal. Fig.
3 is a block diagram illustrating a detailed configuration of an apparatus for decoding a multi-channel signal according to an embodiment of the present invention.
4 is a flowchart illustrating a method of encoding a multi-channel signal according to an embodiment of the present invention.
FIG. 5 is a flowchart illustrating a method of decoding a multi-channel signal according to an embodiment of the present invention. Referring to FIG.
6 is an example of generating a mono signal by downmixing a stereo signal using an OPD estimation and a CLD offset.
7 is a view showing an example of modifying the phase of the OPD value.
8 is a flowchart illustrating a method of encoding a multi-channel signal according to another embodiment of the present invention.
9 is a flowchart illustrating a method of decoding a multi-channel signal according to another embodiment of the present invention.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to or limited by the embodiments. Like reference symbols in the drawings denote like elements.

1 is a block diagram showing a detailed configuration of an apparatus for encoding a multi-channel signal according to an embodiment of the present invention.

The apparatus 100 for encoding a multi-channel signal according to an embodiment of the present invention includes a parameter extracting unit 110, a parameter encoding unit 120, a downmixing unit 130, a mono signal encoding unit 140, And a generating unit 150. Here, according to an embodiment of the present invention, the apparatus 100 for encoding a multi-channel signal may further include a parameter modifier 160. Hereinafter, the function of each component will be described in detail.

Here, the multi-channel signal means a signal of a plurality of channels. In the present specification, each of a plurality of channels included in the multi-channel signal is referred to as a channel signal.

Hereinafter, for convenience of description, it is assumed that a multi-channel signal input to the multi-channel signal encoding apparatus 100 is a stereo signal including a left channel signal and a right channel signal. However, the apparatus 100 for encoding a multi-channel signal according to an exemplary embodiment of the present invention can be used not only for a stereo signal but also for encoding a multi-channel signal. .

The parameter extracting unit 110 extracts a plurality of parameters indicating the characteristic relationship between the left channel signal and the right channel signal constituting the stereo signal. The plurality of parameters may include the above-mentioned CLD, ICC, IPD, OPD, and the like. Here, IPD and OPD are examples of phase parameters related to the phase information between the left channel signal and the right channel signal.

The parameter encoding unit 120 encodes the extracted plurality of parameters.

In this case, since OPD can be estimated from other parameters, according to an embodiment of the present invention, the parameter encoding unit 120 encodes only CLD, ICC, and IPD among the extracted parameters, OPD does not encode . That is, the multi-channel signal encoding apparatus 100 can reduce the bit amount of the transmitted bit stream by not encoding and transmitting the OPD. A more detailed description of the OPD estimation will be made with reference to the description of the multi-channel signal decoding apparatus 300 of FIG.

In addition, the parameter encoding unit 120 may quantize a plurality of extracted parameters to reduce the amount of bits allocated to the encoding of the plurality of parameters, and encode the plurality of quantized parameters. If the parameter encoding unit 120 encodes only CLD, ICC, and IPD among a plurality of parameters, the parameter encoding unit 120 quantizes only CLD, ICC, and IPD, and quantizes CLD, ICC, and IPD Can be encoded.

The downmixing unit 130 downmixes the stereo signal and outputs a mono signal.

Down-mixing is to generate a mono signal of one channel from a stereo signal of two or more channels. By down-mixing, the bit amount of the bit stream generated in the encoding process can be reduced. At this time, the mono signal may be a signal representative of the stereo signal. In other words, in the multi-channel signal encoding apparatus 100, only the mono signal can be coded and transmitted without encoding each of the left channel signal and the right channel signal included in the stereo signal.

For example, the magnitude of the mono signal can be obtained as an average value of the magnitudes of the left channel signal and the right channel signal, and the phase of the mono signal can be obtained as an average value of the phases of the left channel signal and the right channel signal.

The mono signal encoding unit 140 encodes the mono signal output from the downmixing unit 130.

As an example, when the stereo signal is a voice signal, the mono signal encoding unit 120 may encode the mono signal in a CELP (Code Excited Linear Prediction) method.

As another example, when the stereo signal is a music signal, the mono signal encoding unit 120 may encode a mono signal using a method similar to the conventional MPEG-2/4 AAC or mp3.

The bitstream generator 150 generates an encoded bitstream for a stereo signal using a plurality of encoded parameters and an encoded monaural signal.

As described above, the apparatus 100 for encoding a multi-channel signal extracts a mono signal and a plurality of parameters from a stereo signal in order to reduce the amount of transmitted bits, and encodes the extracted mono signal and extracted parameters send. Also in this case, in order to further reduce the bit amount used for transmission of a plurality of parameters, the multi-channel signal encoding apparatus 100 encodes only CLD, ICC, and IPD excluding OPD among a plurality of parameters and transmits .

However, in this case, since the stereo signal itself is not encoded and transmitted, deterioration of sound quality may occur when reproducing the stereo signal. Therefore, there is a need for a method capable of reducing the amount of bits transmitted while minimizing deterioration of sound quality. Hereinafter, embodiments of the operation of the multi-channel signal encoding apparatus 100 for reducing deterioration of sound quality will be described. The dashed arrows in FIG. 1 may be used to describe an apparatus 100 for coding a multi-channel signal according to another embodiment of the present invention. The apparatus 100 for encoding a channel signal according to another embodiment of the present invention will be described in detail later.

Modification of the phase parameters indicating the phase information between the left channel signal and the right channel signal

As described above, when only the CLD, ICC, and IPD among a plurality of parameters are encoded and transmitted to the decoding end in the multi-channel signal encoding apparatus 100, OPD is estimated using CLD and IPD in the decoding end . In this case, if the estimated OPD changes abruptly in successive frames, unwanted noise may be generated. Hereinafter, the concept of noise generation according to changes in phase parameters will be described in detail with reference to FIG.

Fig. 2 is a conceptual diagram for explaining a change in a phase parameter in successive frames included in a stereo signal. Fig.

2 (a) shows the relationship between the phase parameters IPD and OPD, the left channel signal, the right channel signal, and the mono signal. Here, "L" represents a left channel signal on the frequency domain, "R " represents a right channel signal on the frequency domain, and" M " represents a downmixed mono signal. At this time, IPD and OPD can be calculated through the following equations (1) and (2).

Here, L · R denotes the dot product of the left channel signal and the right channel signal, IPD denotes an angle formed between the left channel signal and the right channel signal, and * denotes a complex conjugate.

L denotes an inner product of a left channel signal and a mono signal, OPD denotes an angle between a left channel signal and a mono signal, and * denotes a complex conjugate.

FIG. 2B shows an example in which the phase parameters IPD and OPD change abruptly in successive frames.

2B, "Frame" denotes a current frame, and "Frame-1" denotes a frame one frame before the current frame (hereinafter referred to as "previous frame").

As shown in FIG. 2 (b), when the IPD is changed around 180 ° in the previous frame and the current frame, the IPD greatly changes from 180 ° to -180 ° on the basis of the left channel signal, Changes rapidly from 90 DEG to -90 DEG based on the left channel signal. Such a sudden change of the IPD and OPD causes undesired noise in the reproduction of the stereo signal. Therefore, in order to reduce the noise generated during reproduction of the stereo signal and to improve the sound quality of the stereo signal, the phase parameter related to the phase information between the left channel signalized right channel signals should be corrected.

To this end, the multi-channel signal encoding apparatus 100 modifies the phase parameters extracted by the parameter extracting unit 110 to adjust the degree of change of the phase parameters in the consecutive frames, thereby reducing the noise generated in the reproduction of the stereo signal . At this time, the parameter modification can be performed in the parameter modification unit 160 included in the multi-channel signal encoding apparatus 100. [

In one example, the parameter modifier 160 may modify IPD to 0 DEG when CLD is zero and IPD is 180 degrees. In other words, when there is no energy difference between the left channel signal and the right channel signal and the angle between the left channel signal and the right channel signal is 180 degrees, IPD is forcedly set to 0 degrees.

In other words, when the IPD continuously changes near 180 degrees as shown in FIG. 2 (b), the multi-channel signal encoding apparatus 100 corrects the IPD to 0 degrees at the time when the IPD becomes 180 degrees And transmits the modified IPD to the decoding end. In this case, the OPD estimated at the decoding end does not change from -90 DEG to -90 DEG but changes stepwise in the order of 90 DEG, 0 DEG, and -90 DEG, so that the sharpness of the phase information generated in the decoding step of the stereo signal So that the change can be prevented.

Selective encoding of phase parameters

As described above, the multi-channel signal encoding apparatus 100 quantizes a plurality of extracted parameters (in particular, phase parameters) to reduce the amount of bits allocated to the encoding of a plurality of parameters, Parameters can be encoded and transmitted to the decoding end.

However, if the stereo signal is reconstructed and reproduced using the phase parameters at the decoding end when the phase information continuously changes in successive frames included in the stereo signal (i.e., when the degree of change of the phase parameter is small) Quantization of the parameters and resulting discontinuous phase values can cause deterioration of sound quality.

Therefore, the apparatus 100 for encoding a multi-channel signal according to an embodiment of the present invention can determine whether to encode a phase parameter based on the degree of change (continuity) of phase information between a plurality of frames included in a stereo signal. That is, when it is determined that the phase information between a plurality of frames included in the stereo signal is continuous, the phase information is not encoded, and when it is determined that the phase information is not continuous, the phase information can be encoded. At this time, the determination of whether or not the phase parameter is to be encoded may be performed in the parameter encoding unit 120.

In this case, according to an embodiment of the present invention, the parameter encoding unit 120 may store the phase information value of the current frame, the phase information value of the frame one frame before the current frame, and the phase information value of the frame two frames before the current frame The continuity of the phase information can be determined using the value. That is, the parameter encoding unit 110 uses the phase information value of the n-th frame, the phase information value of the (n-1) th frame, and the phase information value of the (n-2) It can be judged.

As an example, the parameter encoding unit 120 calculates a first phase difference value which is a difference between a two-fold value of a phase information value of a frame one frame before the current frame and a phase information value of a frame two frames before the current frame , Calculates a second phase difference value that is a difference between the phase information value of the current frame and the first phase difference value, and determines that the phase information is not continuous if the second phase difference value is larger than a predetermined value It is determined that the information does not change slowly), and the encoding of the phase parameter can be determined. This can be expressed by the following equation (3).

PhasePrev [] is the phase information value of the frame one frame before the current frame, PhasePrev2 [] is the phase information value of the frame two frames before the current frame, PhaseError [] is the phase information value of the current frame, The second phase difference value, band, means a frequency band to which the phase information is applied.

Therefore, when the PhaseError [band] is larger than a preset value, the parameter encoding unit 120 decides to encode the phase information, and when the PhaseError [band] is smaller than or equal to a predetermined value, do.

According to another embodiment of the present invention, the parameter encoding unit 120 determines whether or not the phase information is continuous using the difference between the phase information value of the previous frame and the phase information value of the current frame, Based on this, it is possible to determine whether or not the phase parameter is encoded.

As an example, the parameter encoding unit may calculate the difference between the phase information of the current frame and the phase information of the previous frame, and calculate the slope thereof to determine whether the phase information is continuous or not .

Here, Slope [] denotes a difference between a phase information value of a current frame and a phase information value of a frame one frame before, and a band denotes a frequency band to which phase information is applied.

When the slope [band] varies with a certain slope or more, noise may be generated due to discontinuity of phase information due to quantization. Therefore, when the slope of slope [band] And decides the coding of the phase information when the slope of the slope [band] is smaller than or equal to a predetermined value.

In the calculations of Equations (3) and (4), the parameter coding unit 120 calculates the first phase difference value, the second phase difference, and the second phase difference considering the fact that the phase information changes to wrapping property on the basis of 360 degrees. Difference value, and the phase difference value between the current frame and the frame one frame before. For example, when the phase difference value is 370 °, the parameter encoding unit 120 calculates the phase difference value at -10 ° in consideration of the period of 360 °.

As another example, it is possible to determine whether or not the phase information is encoded by combining the parameter Encoder 120 with PhaseError [band] and slope [band].

According to another embodiment of the present invention, the parameter encoding unit 120 may determine whether to encode phase information by combining PhaseError [band] and slope [band].

In addition to the continuity of the phase information, the parameter encoding unit 120 can determine whether to encode the phase parameter (more accurately, the IPD included in the phase parameter) based on the ICC value extracted by the parameter extraction unit 110. [

The parameter extracting unit 110 may extract the ICC using the IPD or extract the ICC without using the IPD. If the difference between the ICC extracted using the IPD and the ICC extracted using the IPD If it is larger than the preset value, it can be interpreted that the IPD has a meaning more important than the ICC in the decoding step of the stereo signal. On the contrary, if the difference between the ICC extracted using the IPD and the ICC extracted using the IPD , It can be interpreted that ICC has more significance than IPD.

Therefore, according to the embodiment of the present invention, the parameter encoding unit 120 can determine the encoding of the IPD when the difference between the extracted ICC and the extracted ICC is not larger than a predetermined value, .

In this case, the multi-channel signal encoding apparatus 100 can encode the ICC considering IPD and IPD and transmit it to the decoding end. In the decoding end, the stereo signal is restored using the ICC considering IPD and IPD, Can be restored.

That is, in restoring the stereo signal, the decoding unit adjusts the degree of mixing of the decorrelated signal and the restored mono signal corresponding to the vertical vector component of the restored mono signal using the ICC. Therefore, when the stereo signal is restored by using the ICC considering the IPD at the decoding end, it is possible to prevent the decorrelated signal restored mono signal from being excessively mixed due to the difference in phase information, thereby restoring the stereo signal close to the original sound .

As an example, the parameter extracting unit 120 can extract an ICC considering IPD according to the following equation (5).

That is, the correlation between the left channel signal and the right channel signal is calculated by compensating the phase information, and the ICC considering the IPD can be calculated by taking only the real value of the calculated correlation.

As another example, the parameter extracting unit 120 can extract the ICC considering the IPD according to the following expression (6).

Here, Q means quantization and Q ^-1 means inverse quantization, respectively.

That is, when a stereo signal is reconstructed at a decoding end using the ICC extracted according to Equation (6), it is possible to compensate for an error that may be caused by the quantization of the above-mentioned phase parameter.

As another example, the parameter extraction unit 120 can extract the ICC considering the IPD according to the following equation (7).

Optional change of phase parameter quantization method

As described above, the multi-channel signal encoding apparatus 100 can encode the quantized phase parameters and transmit them to the decoding end. Therefore, if the phase parameters are uniformly encoded and transmitted to the decoding end, the multi-channel signal encoding apparatus 100 can selectively change the quantization scheme to prevent deterioration of sound quality due to quantized phase parameters have.

In other words, if the phase parameters are quantized at wide intervals despite the small degree of change in the phase information (i.e., the phase information is continuously changed), deterioration in the sound quality of the stereo signal reproduced at the decoding end due to discontinuous phase values Therefore, the apparatus 100 for encoding a multi-channel signal according to an embodiment of the present invention can determine a quantization type of a phase parameter based on continuity of phase information. At this time, the determination of the quantization type may be performed in the parameter encoding unit 120. [

That is, when it is determined that the phase information is not continuous, the parameter encoding unit 120 quantizes the phase parameter according to the first quantization type, and if the phase information is determined to be continuous, the phase parameter is quantized according to the second quantization type can do.

In this case, the number of quantization levels according to the first quantization type and the number of quantization levels according to the second quantization type may be different from each other.

In addition, the representative value at the quantization level according to the first quantization type (i.e., the value quantized at the quantization level) and the representative value at the quantization level according to the second quantization type may be different from each other.

Therefore, in the above case, the quantization error according to the first quantization type and the quantization error according to the second quantization type may be different from each other. Here, the quantization error means a difference value between a quantized value and a non-quantized value.

As an example, when the phase information is continuous, the parameter encoding unit 120 can quantize the phase parameters at finer intervals, thereby minimizing deterioration of the sound quality of the stereo signal generated at the decoding end. In this case, the number of quantization levels of the first quantization type is smaller than the number of quantization levels of the second quantization type.

In this case, whether or not the phase information is continuous can be determined based on Equations (3) to (4) above.

When the parameter encoding unit 120 encodes the phase parameter by selectively applying the quantization type, the bitstream generating unit 150 can generate a bitstream using the determined quantization type information. In this case, it is possible to perform inverse quantization by referring to the quantization type information at the decoding end that has received the beast stream. If the multi-channel signal encoding apparatus 100 does not transmit the phase information to the decoding end, the bitstream generating unit 150 does not include the quantization type information in the bitstream, but does not include the bit that does not include the quantization type information The decoding unit that receives the stream can perform inverse quantization without referring to the quantization type information. A more detailed description of the inverse quantization performed in the decoding stage will be described with reference to a description of the multi-channel signal decoding apparatus 300 of FIG.

The following [Table 1] and [Table 2] show quantization angle information when the number of quantization levels of the first quantization type is eight and the number of quantization levels of the second quantization type is sixteen.

Embodiments of the operation of the apparatus 100 for encoding a multi-channel signal in order to reduce the bit amount of the transmitted bit stream and reduce deterioration of sound quality have been described above. Hereinafter, an apparatus for decoding a multi-channel signal according to an embodiment of the present invention will be described in detail with reference to FIG.

3 is a block diagram illustrating a detailed configuration of an apparatus for decoding a multi-channel signal according to an embodiment of the present invention.

The apparatus 300 for decoding a multi-channel signal according to an exemplary embodiment of the present invention includes a mono signal decoding unit 310, a parameter decoding unit 320, a parameter estimating unit 330, an upmixing unit 340, (350). Hereinafter, the function of each component will be described in detail.

Hereinafter, for the sake of convenience, it is assumed that the bit stream input to the multi-channel signal decoding apparatus 300 is a coded bit stream of a stereo signal.

It is also assumed that the input bitstream is demultiplexed with a coded mono signal and a plurality of coded parameters.

The mono signal decoding unit 310 restores the mono signal, which is a downmix signal of the multi-channel signal, from the encoded bit stream of the stereo signal. Specifically, when the mono signal is coded in the time domain, the mono signal decoding unit 310 decodes the coded mono signal in the time domain, and when the mono signal is coded in the frequency domain, It can be decoded.

The parameter decoding unit 320 reconstructs a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting the multi-channel signal from the encoded bit stream of the stereo signal. At this time, a plurality of parameters may include CLD, ICC, and IPD, but not OPD.

The parameter estimator 330 estimates the OPD using the plurality of reconstructed parameters.

Hereinafter, the operation of the parameter estimator 330 for estimating the OPD will be described in detail. . Hereinafter, the formulas described below are only examples of the present invention, and it will be apparent to those skilled in the art that the formulas described below can be modified.

First, the parameter estimator 330 obtains the first intermediate variable c using the CLD according to the following equation (8).

Here, b represents an index of a frequency band. As shown in Equation (8), the first intermediate variable c can be obtained by expressing the number obtained by dividing the IID value in the specific frequency band by 20 in an exponential form of 10. At this time, the second intermediate variable c ₁ and the third intermediate variable c ₂ can be obtained by using the first intermediate variable c as shown in the following equations (9) and (10).

That is, the third intermediate variable c ₂ can be obtained by multiplying the value of the second intermediate variable c ₁ by c.

Next, the parameter estimator 330 obtains the first right channel signal and the first left channel signal using the restored mono signal and the second intermediate variable and the third intermediate variable obtained by Equations (9) and (10) . The first right channel signal and the first left channel signal can be expressed by the following equations (11) and (12).

는 제2 중간 변수 c₁과 복원된 모노 신호 M의 곱으로 나타낼 수 있다.Where n is the time slot index and k is the parameter band index. The first right channel signal

Can be expressed as the product of the second intermediate variable c ₁ and the restored mono signal M.

는 제2 중간 변수 c₂와 복원된 모노 신호 M의 곱으로 나타낼 수 있다.The first left channel signal

Can be expressed as the product of the second intermediate variable c ₂ and the restored mono signal M.

라고 하면, 제1 모노 신호

는 제1 우채널 신호

및 제2 좌채널 신호

를 이용하여 다음 수학식 13과 같이 나타낼 수 있다. At this time,

, The first mono signal

Lt; RTI ID = 0.0 >

And the second left channel signal

The following equation (13) can be used.

Further, using Equations (10) to (13), the fourth intermediate variable p according to the time slot and the parameter band can be obtained by the following Equation (14).

라 할 때, OPD는 다음 수학식 15와 같이 구할 수 있다.Here, the fourth intermediate variable p is a value obtained by dividing the sum of the sizes of the first left channel signal, the first right channel signal, and the first mono signal by two. At this time, the value of OPD

, The OPD can be obtained by the following equation (15).

라 할 때,

은 다음 수학식 16과 같이 구할 수 있다.Also, the value corresponding to the difference between OPD and IPD

In other words,

Can be obtained by the following equation (16).

은 복호화된 모노 신호와 업믹싱될 좌채널 신호 사이의 위상 차이고, 수학식 16에서 구한 값인

는 복호화된 모노 신호와 업믹싱될 우채널 신호 사이의 위상 차를 나타낸다.The value of OPD obtained from the equation (15)

Is the phase difference between the decoded mono signal and the left channel signal to be upmixed,

Represents the phase difference between the decoded mono signal and the right channel signal to be upmixed.

As described above, the parameter estimator 330 generates the first left channel signal and the first right channel signal for the left channel signal and the right channel signal from the restored mono signal using the IID indicating the difference between channels of the stereo signal And generates a first mono signal from the first left channel signal and the first right channel signal using the IPD representing the phase difference between channels of the stereo signal, and outputs the generated first left channel signal, the first right channel signal, The value of the OPD indicating the phase difference between the restored mono signal and the stereo signal using the first mono signal can be estimated.

The upmixing unit 340 upmixes the mono signal using the restored at least one parameter and the estimated OPD.

Upmixing corresponds to downmixing by generating more than two channels of stereo signals from a mono signal of one channel. Hereinafter, the specific operation of the upmixing unit 340 upmixing the mono signal using CLD, ICC, IPD, and OPD will be described.

일 때, 제2 및 제3 중간 변수 c₁ 및 c₂를 이용하여 제1 위상

및 제2 위상

을 다음 수학식 17 및 18과 같이 구할 수 있다.First, the upmixer 340 multiplies the value of ICC by

, The second and third intermediate variables c ₁ and c ₂ are used to determine the first phase

And the second phase

Can be obtained by the following equations (17) and (18).

, 수학식 16에서 구한 값인

을 이용하여 아래의 수학식 19 및 수학식 20과 같이 업믹싱된 좌채널 신호 및 우채널 신호를 구할 수 있다.Next, the upmixing unit 340 multiplies the first and second phases, the second and third intermediate values obtained through Equations (18) and (19) when the restored mono signal is M and the decorrelated signal is D, The values of the variables c ₁ and c ₂ and the value of OPD obtained from the equation (15)

, The value obtained from the equation (16)

The left channel signal and the right channel signal upmixed as shown in Equation (19) and (20) below can be obtained.

As described above, the apparatus 300 for decoding a multi-channel signal according to an embodiment of the present invention estimates the OPD value using the transmitted parameters and restores the stereo signal using the estimated OPD parameter and other transmitted parameters .

However, as mentioned in the description of FIG. 2, when the OPD estimated using the transmitted parameters is abruptly changed in successive frames, noise may be generated and sound quality may deteriorate. Therefore, When the phase parameter is transmitted without modifying the phase parameter, the phase parameter is corrected in the multi-channel signal decoding apparatus 300 to reduce the noise.

To this end, the apparatus 300 for decoding a multi-channel signal according to an embodiment of the present invention corrects the estimated OPD and restores the stereo signal using the modified OPD and the restored parameters.

If the recovered plurality of parameters includes CLD and IPD, the apparatus 300 for decoding a multi-channel signal according to an embodiment of the present invention can modify the OPD based on CLD and IPD. In this case, the modification of the parameter is performed by the parameter correction unit 350. [

In one example, the parameter modifier 350 may modify the estimated OPD to 0 DEG when the reconstructed IPD is 180 DEG.

In another example, the parameter modifier 350 may modify the estimated OPD using the CLD if the reconstructed IPD is not 180 [deg.], Where the modified OPD is a value between the restored OPD and 0 [ Or a value between -180 DEG and -180 DEG.

In other words, when the restored IPD is changed near 180 °, the estimated OPD can be abruptly changed from about 90 ° to around -90 °, and the parameter modifier 330 prevents such a sudden change of the OPD , OPD is set to 0 DEG when IPD is 180 DEG and OPD is set to any value between 90 DEG and 0 DEG or between -90 DEG and 0 DEG when IPD is a value near 180 DEG, For example, 67.5 DEG or -67.5 DEG. Accordingly, the OPD does not change from 90 DEG to -90 DEG, but is changed step by step in the order of 67.5 DEG, 0 DEG and -67.5 DEG, so that the abrupt change of the phase information can be prevented.

The modification of the OPD described above can be performed according to the following expression (21).

Further, according to another embodiment of the present invention, the parameter correction unit 350 may modify the OPD so that the estimated OPD is filtered to reduce the variation of the estimated OPD.

For example, the parameter modifier 350 may modify the estimated OPD using Infinite Impulse Response (IIR).

Further, the parameter modifier 350 may filter the estimated OPD based on the following equation (22).

는 현재 프레임에서의 특정 주파수 대역에 포함되는 신호에 대한 위상 정보,

는 현재 프레임의 1프레임 이전의 프레임에서의 특정 주파수 대역에 포함되는 신호에 대한 위상 정보,

는 0보다 크고 1보다 작은 임의의 실수,

는 현재 프레임에서의 특정 주파수 대역에 포함되는 신호의 필터링된 위상 정보를 각각 의미한다. here,

The phase information of the signal included in the specific frequency band in the current frame,

The phase information of the signal included in the specific frequency band in the frame one frame before the current frame,

Is an arbitrary real number greater than 0 and less than 1,

Represents the filtered phase information of a signal included in a specific frequency band in the current frame, respectively.

에 제1 가중치(

)를 부여하고,

에 제2 가중치(

)를 부여하고 가중치가 부여된

와 가중치가 부여된

를 더하여 추정된 OPD의 변화량이 감소되도록 OPD를 수정할 수 있다.That is, the parameter correction unit 360

The first weight (

),

The second weight (

) And the weighted

And weighted

The OPD can be modified so that the estimated amount of change in OPD is reduced.

Also, in the above case, whether to apply filtering on the estimated OPD can be determined at the encoding end. The encoding unit may include information on performing filtering in the bitstream and may transmit the information to the decoding apparatus 300 of the multi-channel signal. The parameter modifier 350 may determine whether to perform the filtering according to the filtering information.

As described in the description of FIG. 1, at the encoding end, it is possible to select a quantization type based on continuity of phase information, and generate a bitstream including quantized phase parameters and quantization type information according to the selected quantization type have.

If the apparatus 300 for decoding a multi-channel signal according to an embodiment of the present invention receives a bitstream including quantized phase parameters and quantization type information, the parameter decoding unit 320 receives the quantized phase (Hereinafter referred to as a first phase parameter) and quantization type information, and to dequantize the first phase parameter based on the restored quantization type information to calculate a second phase parameter.

In this case, the upmixing unit 340 may upmix the mono signal using the remaining parameters except for the second phase parameter and the second phase parameter.

Accordingly, the multi-channel signal decoding apparatus 300 can reduce quantization of phase parameters and deterioration of sound quality due to the discontinuous phase values.

4 is a flowchart illustrating a method of encoding a multi-channel signal according to an embodiment of the present invention.

Referring to FIG. 4, a method of encoding a multi-channel signal according to an embodiment of the present invention includes steps processed in the apparatus 100 for encoding a multi-channel signal shown in FIG. Therefore, even if omitted below, the description of the multi-channel signal encoding apparatus 100 shown in FIG. 1 also applies to the multi-channel signal encoding method according to an embodiment of the present invention.

First, in step S410, a plurality of parameters representing characteristic information between a plurality of channels constituting the multi-channel signal are extracted.

In step S420, the phase information regarding the phase information between a plurality of channels among the plurality of parameters is corrected.

According to one embodiment of the present invention, the phase parameter may comprise an IPD.

Further, according to an embodiment of the present invention, the plurality of parameters include CLD, and in step S410, when CLD is 0 and IPD is 180, IPD can be modified to 0 deg.

In step S430, a plurality of parameters including the corrected phase parameters are encoded.

In step S440, a mono signal obtained by downmixing the multi-channel signal is encoded.

In step S450, an encoded bit stream for the multi-channel signal is generated using the plurality of encoded parameters and the encoded mono signal.

FIG. 5 is a flowchart illustrating a method of decoding a multi-channel signal according to an embodiment of the present invention. Referring to FIG.

Referring to FIG. 5, a method for decoding a multi-channel signal according to an embodiment of the present invention includes steps performed in an apparatus 300 for decoding a multi-channel signal shown in FIG. Therefore, even though omitted in the following description, the description of the multi-channel signal decoding apparatus 300 shown in FIG. 3 is applied to a method of encoding a multi-channel signal according to an embodiment of the present invention.

First, in step S510, a mono signal, which is a downmix signal of the multi-channel signal, is recovered from the coded bit stream of the multi-channel signal.

In step S520, a plurality of parameters indicating characteristic relationships between a plurality of channels constituting the multi-channel signal are restored from the bit stream.

In step S530, OPD is estimated using the plurality of reconstructed parameters.

In step S540, the estimated OPD is corrected.

According to one embodiment of the present invention, the plurality of parameters include CLD and IPD, and in step S540 OPD can be modified based on CLD and IPD.

In this case, in the step S540, when the IPD is 180 degrees, the OPD can be modified to 0 degrees. If the IPD is not 180 °, the OPD is corrected using the CLD, and the modified OPD is set to a value between the restored OPD and 0 ° or a value between the restored OPD and -180 ° Or the like.

According to another embodiment of the present invention, in step S540, the estimated OPD may be filtered to modify the OPD so that the estimated amount of change of the OPD is reduced. In this case, the OPD estimated using the IIR filter may be filtered in step S540.

In step S550, the mono signal is upmixed using the restored at least one parameter and the modified OPD.

1, the apparatus 100 for encoding a multi-channel signal according to another embodiment of the present invention includes a parameter extracting unit 110, a downmixing unit 130, a bitstream generating unit 150 ) And the parameter correction unit 160. [0050]

Here, the multi-channel signal means a signal of a plurality of channels. In the present specification, each of a plurality of channels included in the multi-channel signal is referred to as a channel signal.

For convenience of explanation, it is assumed that the multi-channel signal input to the multi-channel signal encoding apparatus 100 is a stereo signal including a left channel signal and a right channel signal. However, it is to be understood that the apparatus 100 for encoding a multi-channel signal according to another embodiment of the present invention can be used not only for a stereo signal but also for encoding a multi-channel signal. .

The parameter extracting unit 110 extracts a plurality of parameters indicating the characteristic relationship between the left channel signal and the right channel signal constituting the stereo signal. The plurality of parameters may include the above-mentioned CLD, ICC, IPD, OPD, and the like. Here, IPD is an example of a phase parameter related to phase information between a left channel signal and a right channel signal. The OPD is an example of a phase parameter relating to phase information between a mono signal and a left channel signal or a mono signal and a right channel signal to be described later.

A parameter modifier (160) modifies a phase parameter relating to phase information between the plurality of channels among the plurality of parameters. In this case, the plurality of parameters may include channel level differences (CLD) between the plurality of channels, and the parameter modifier 160 adds a CLD offset to the value of the CLD, (OPD) of the signal and the phase difference between the plurality of channels.

For example, in the above-mentioned equation (21), the OPD can be modified by multiplying the value of the CLD offset by the value of the second intermediate variable c ₁ or the third intermediate variable c ₂ which can be determined according to the value of CLD. By adding this CLD offset, the phase of the mono signal, which is the downmix signal of the stereo signal, can be determined. That is, it is possible to increase the size of the left channel signal or the right channel signal only in the calculation of the OPD. This example can be expressed as Equation 23 below. 6 is an example of generating a mono signal by downmixing a stereo signal using an OPD estimation and a CLD offset. That is, the dotted line box 600 shows a state in which a mono signal is generated by increasing the size of the left channel signal. Here, the generation of the mono signal will be described in more detail later.

At this time, even if the CLD offset is added, the IPD can always be maintained and the slope of the phase trajectory can be determined according to the value of the CLD offset. Therefore, the phase discontinuity can be eliminated by using the CLD offset, and the downmixing result can be restored without distortion. At this time, the phase discontinuity can be removed by upmixing the downmixed mono signal by adding the CLD offset even in decoding. Decoding will be described in more detail later.

The value of this CLD offset can be set, for example, so that the difference between adjacent frames is smaller than the phase quantization bin, based on IPD 180 °, which represents the largest difference. Assuming that the value of CLD is 1, the CLD offset can have a square root of 2 so that the difference between adjacent frames in the coarse quantization is less than 45 degrees of phase quantization bin. Also, assuming that the CLD value is 1, the CLD offset may have a value of 1.8477 so that the difference between adjacent frames in fine quantization is smaller than the phase quantization bin 22.5 DEG. Each of these examples can be expressed by the following equations (24) and (25) using the following Equation (23).

Here, opd _{ipd = 180} may have a value of zero.

Further, in another embodiment, the parameter modifier 160 may remove phase discontinuities by modifying the phase by modifying the value of the instant OPD at which the phase discontinuity appears. In this case, if the difference between the OPD value of the frame one frame before the current frame and the OPD value of the current frame is greater than or equal to a predetermined value, the parameter modifier 160 may modify the OPD value of the current frame. For example, if the difference between the OPD value of the frame one frame before the current frame and the OPD value of the current frame is greater than or equal to 90 degrees, the parameter correcting unit 160 corrects the value of the OPD by 180 degrees to eliminate the phase discontinuity . 7 is a view showing an example of modifying the phase of the OPD value. In this case, the x-axis represents the time and the y-axis represents the phase value in the first graph 710 and the second graph 720, respectively. That is, as in the second graph 720, the phase discontinuity can be eliminated by correcting the value of OPD by 180 degrees as soon as the phase discontinuity of OPD appears. The first arrow 721 and the second arrow 722 indicate that the value of OPD has been changed by modifying the value of OPD by 180 degrees so that the phase discontinuity has been removed. At this time, in order to modify the value of OPD by 180 °, it is possible to add or subtract 180 ° (π) to the value of OPD. The modification of this OPD value can be expressed as Equation 26 below.

The downmixing unit 130 downmixes the multi-channel signal through the modified phase parameters to generate a mono signal. That is, the modified phase parameters may be transmitted to the downmixing unit 130, and the downmixing unit 130 may transmit the modified phase parameters to the downmixing unit 130, Channel signal through a phase parameter transmitted through the demodulator 160 and generate a mono signal by downmixing the multi-channel signal. Here, down-mixing is to generate a mono signal of one channel from a stereo signal of two or more channels, and it is possible to reduce the bit amount of the bit stream generated in the encoding process by down-mixing. At this time, the mono signal may be a signal representative of the stereo signal. In other words, in the multi-channel signal encoding apparatus 100, only the mono signal can be coded and transmitted without encoding each of the left channel signal and the right channel signal included in the stereo signal. For example, the magnitude of the mono signal can be obtained as an average value of the magnitudes of the left channel signal and the right channel signal, and the phase of the mono signal can be obtained as an average value of the phases of the left channel signal and the right channel signal. At this time, by modifying the parameters by the parameter correction unit 160, the magnitudes of the left channel signal and the right channel signal or the phase of the left channel signal and the right channel signal can be changed, and as the magnitude or phase is changed, The magnitude and phase of the magnetic field can also be changed. In another embodiment, the downmixing unit 130 may shift the phase of the left channel signal and the right channel signal based on the IPD and the OPD, respectively, and express the result as a sum of two channel signals. In this case, a gain value based on CLD or ICC can be used to adjust the size of the mono signal. This example can be expressed as Equation (27). In this case, the downmixing unit 130 may receive the IPD, the CLD, and the ICC from the parameter extraction unit 110, as indicated by a dotted arrow connected to the downmixing unit 130 in the parameter extraction unit 110 of FIG. That is, IPD, CLD, and ICC may be included in a plurality of parameters extracted by the parameter extracting unit 110.

The bitstream generator 150 encodes the plurality of parameters except for the modified phase parameter and the generated mono signal to generate a bitstream. In this case, the mono signal may be encoded in a CELP (Code Excited Linear Prediction) method when the stereo signal is a voice signal. As another example, when the stereo signal is a music signal, the mono signal can be encoded using a method similar to the conventional MPEG-2/4 AAC or mp3.

At this time, the modified phase parameters may include OPD, which is a parameter related to the phase difference between the mono signal and the plurality of channels. Since OPD can be estimated from other parameters, according to another embodiment of the present invention, the bitstream generator 150 encodes only CLD, ICC, and IPD among a plurality of extracted parameters, OPD does not encode have. In other words, the apparatus 100 for encoding a multi-channel signal according to another embodiment can reduce the bit amount of a bitstream to be transmitted by not encoding and transmitting OPD. A more detailed description of the OPD estimation will be made with reference to the description of the multi-channel signal decoding apparatus 300 of FIG.

In addition, the bitstream generator 150 may quantize a plurality of extracted parameters to reduce the amount of bits allocated to the encoding of the plurality of parameters, and may encode a plurality of quantized parameters. If the bitstream generation unit 150 encodes only CLD, ICC, and IPD among a plurality of parameters, the bitstream generation unit 150 quantizes only CLD, ICC, and IPD, and quantizes CLD, ICC, IPD can be encoded.

As described above, the apparatus 100 for encoding a multi-channel signal extracts a mono signal and a plurality of parameters from a stereo signal in order to reduce the amount of transmitted bits, and encodes the extracted mono signal and extracted parameters send. Also in this case, in order to further reduce the bit amount used for transmission of a plurality of parameters, the multi-channel signal encoding apparatus 100 encodes only CLD, ICC, and IPD excluding OPD among a plurality of parameters and transmits . At this time, since the stereo signal itself is not coded and transmitted, deterioration of sound quality may occur during reproduction of the stereo signal. Therefore, by adding a CLD offset or modifying the OPD value in the OPD calculation, a mono signal can be generated, thereby reducing the amount of bits and eliminating the phase discontinuity and minimizing deterioration of sound quality.

Referring again to FIG. 3, an apparatus 300 for decoding a multi-channel signal according to another embodiment of the present invention may include only an upmixing unit 340 and a parameter modifying unit 350. Hereinafter, the function of each component will be described in detail.

The parameter modifier 350 modifies parameters related to the phase difference between the mono signal and the multi-channel signal, which are the downmix signals of the multi-channel signals. Here, the parameter related to the phase difference may include OPD estimated through a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting the multi-channel signal. At this time, the plurality of parameters may include channel level differences (CLD) between a plurality of channels, and the parameter correction unit 350 may add a CLD offset to the value of the CLD to modify the estimated OPD have.

In addition, the multi-channel signal may include a plurality of frames, and the parameter modifier 350 may determine that the difference between the estimated OPD value of the frame one frame before the current frame and the estimated OPD value of the current frame is greater than or equal to the predetermined value , The estimated OPD value of the current frame can be modified. For example, the predefined value may include 90 [deg.], In which case the parameter correction unit 350 may determine that the difference between the estimated OPD value of the frame one frame before the current frame and the estimated OPD value of the current frame is If it is more than 90 degrees, the OPD value of the current frame can be modified by 180 degrees.

The method of adding the CLD offset or modifying the OPD through the difference of the OPD values between adjacent frames has been described above, and a duplicate description will be omitted.

The upmixing unit 340 upmixes the mono signal using the parameters related to the modified phase difference. That is, the upmixing unit 340 can upmix the mono signal using the modified OPD to eliminate the phase discontinuity, thereby minimizing deterioration of the sound quality. Since the method of upmixing the mono signal has already been described in detail, repetitive description will be omitted.

In this case, the multi-channel signal may be received as an encoded bit stream from the multi-channel signal encoding apparatus 100 described with reference to FIG. 1, and the decoding apparatus 300 of the multi- A mono signal and a plurality of parameters can be restored. At this time, as described above, the parameter OPD related to the phase difference can be estimated through a plurality of parameters. In order to obtain the mono signal from the bitstream and estimate the OPD, the apparatus 300 for decoding the multi-channel signal includes a mono signal decoding unit 310 for decoding the mono signal from the encoded bit stream of the multi-channel signal, A parameter decoding unit 320 for restoring a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting a multi-channel signal, and an overall phase difference (OPD) as a parameter relating to the phase difference using the restored plurality of parameters And a parameter estimator 330 for estimating a parameter.

8 is a flowchart illustrating a method of encoding a multi-channel signal according to another embodiment of the present invention. The method of encoding a multi-channel signal according to the present embodiment can be performed by the apparatus 100 for encoding a multi-channel signal according to another embodiment of the present invention described above. In FIG. 8, a description will be given of a process in which each step is performed by the multi-channel signal encoding apparatus 100, thereby explaining a multi-channel signal encoding method.

Here, the multi-channel signal means a signal of a plurality of channels. In the present specification, each of a plurality of channels included in the multi-channel signal is referred to as a channel signal.

For convenience of explanation, it is assumed that the multi-channel signal input to the multi-channel signal encoding apparatus 100 is a stereo signal including a left channel signal and a right channel signal. However, it is to be understood that the apparatus 100 for encoding a multi-channel signal according to another embodiment of the present invention can be used not only for a stereo signal but also for encoding a multi-channel signal. .

In step 810, the apparatus 100 for encoding a multi-channel signal extracts a plurality of parameters indicating a characteristic relationship between a left channel signal and a right channel signal constituting a stereo signal. The plurality of parameters may include the above-mentioned CLD, ICC, IPD, OPD, and the like. Here, IPD is an example of a phase parameter related to phase information between a left channel signal and a right channel signal. The OPD is an example of a phase parameter relating to phase information between a mono signal and a left channel signal or a mono signal and a right channel signal to be described later.

In step 820, the multi-channel signal encoding apparatus 100 modifies the phase parameters related to the phase information between the plurality of channels among the plurality of parameters. In this case, the plurality of parameters may include energy level difference (CLD) between the plurality of channels, and the multi-channel signal encoding apparatus 100 may add CLD offset to the value of CLD, The overall phase difference (OPD) regarding the mono signal to be described and the phase difference between the plurality of channels can be modified.

For example, in the above-mentioned equation (21), the OPD can be modified by multiplying the value of the CLD offset by the value of the second intermediate variable c ₁ or the third intermediate variable c ₂ which can be determined according to the value of CLD. By adding this CLD offset, the phase of the mono signal, which is the downmix signal of the stereo signal, can be determined. That is, it is possible to increase the size of the left channel signal or the right channel signal only in the calculation of the OPD. This example can be expressed as Equation (23). A method for generating a mono signal by downmixing a stereo signal using an OPD estimation and a CLD offset can be described with reference to FIG. Here, the generation of the mono signal will be described in more detail later.

At this time, even if the CLD offset is added, the IPD can always be maintained and the slope of the phase trajectory can be determined according to the value of the CLD offset. Therefore, the phase discontinuity can be eliminated by using the CLD offset, and the downmixing result can be restored without distortion. At this time, the phase discontinuity can be removed by upmixing the downmixed mono signal by adding the CLD offset even in decoding. The decoding method will be described in more detail later.

The value of this CLD offset can be set, for example, so that the difference between adjacent frames is smaller than the phase quantization bin, based on IPD 180 °, which represents the largest difference. Assuming that the value of CLD is 1, the CLD offset can have a square root of 2 so that the difference between adjacent frames in the coarse quantization is less than 45 degrees of phase quantization bin. Also, assuming that the CLD value is 1, the CLD offset may have a value of 1.8477 so that the difference between adjacent frames in fine quantization is smaller than the phase quantization bin 22.5 DEG. Each of these examples can be expressed as Equations (24) and (25).

Further, in another embodiment, the apparatus 100 for encoding a multi-channel signal may remove the phase discontinuity by modifying the phase by modifying the value of the OPD at the moment when the phase discontinuity appears. At this time, when the difference between the OPD value of the frame one frame before the current frame and the OPD value of the current frame is equal to or larger than a predetermined value, the apparatus 100 for encoding a multi-channel signal can modify the OPD value of the current frame. For example, when the difference between the OPD value of the frame one frame before the current frame and the OPD value of the current frame is equal to or greater than 90 degrees, the encoding apparatus 100 of the multi-channel signal corrects the value of OPD by 180 degrees, Can be removed. An example of modifying the phase can refer to the description of FIG. 7 and the above-described equation (26).

In step 830, the multi-channel signal encoding apparatus 100 downmixes the multi-channel signal through the modified phase parameters to generate a mono signal. Here, down-mixing is to generate a mono signal of one channel from a stereo signal of two or more channels, and it is possible to reduce the bit amount of the bit stream generated in the encoding process by down-mixing. At this time, the mono signal may be a signal representative of the stereo signal. In other words, in the multi-channel signal encoding apparatus 100, only the mono signal can be coded and transmitted without encoding each of the left channel signal and the right channel signal included in the stereo signal. For example, the magnitude of the mono signal can be obtained as an average value of the magnitudes of the left channel signal and the right channel signal, and the phase of the mono signal can be obtained as an average value of the phases of the left channel signal and the right channel signal. At this time, the parameters of the multi-channel signal encoding apparatus 100 may be modified to change the sizes of the left channel signal and the right channel signal or the phase of the left channel signal and the right channel signal. Accordingly, the magnitude and phase of the mono signal can also be changed. In another embodiment, the apparatus 100 for encoding a multi-channel signal may represent the sum of two channel signals after shifting the phase of the left channel signal and the right channel signal based on IPD and OPD. In this case, a gain value based on CLD or ICC can be used to adjust the size of the mono signal. This example can be expressed as Equation (27).

In step 840, the encoding apparatus 100 for a multi-channel signal encodes the plurality of parameters and the generated mono signal except for the modified phase parameter to generate a bitstream. In this case, the mono signal may be encoded in a CELP (Code Excited Linear Prediction) method when the stereo signal is a voice signal. As another example, when the stereo signal is a music signal, the mono signal can be encoded using a method similar to the conventional MPEG-2/4 AAC or mp3.

At this time, the modified phase parameters may include OPD, which is a parameter related to the phase difference between the mono signal and the plurality of channels. OPD can be estimated from other parameters. Therefore, according to another embodiment of the present invention, the multi-channel signal encoding apparatus 100 encodes only CLD, ICC, and IPD among a plurality of extracted parameters, and OPD does not encode . In other words, the apparatus 100 for encoding a multi-channel signal according to another embodiment can reduce the bit amount of a bitstream to be transmitted by not encoding and transmitting OPD. A more detailed description of the OPD estimation can be found in the description of the multi-channel signal decoding apparatus 300 of FIG.

In addition, the multi-channel signal encoding apparatus 100 can quantize a plurality of extracted parameters to reduce the amount of bits allocated to encoding of a plurality of parameters, and encode a plurality of quantized parameters. When the multi-channel signal encoding apparatus 100 encodes only CLD, ICC, and IPD among a plurality of parameters, the multi-channel signal encoding apparatus 100 quantizes only CLD, ICC, and IPD, , ICC, and IPD.

As described above, the apparatus 100 for encoding a multi-channel signal extracts a mono signal and a plurality of parameters from a stereo signal in order to reduce the amount of transmitted bits, and encodes the extracted mono signal and extracted parameters send. Also in this case, in order to further reduce the bit amount used for transmission of a plurality of parameters, the multi-channel signal encoding apparatus 100 encodes only CLD, ICC, and IPD excluding OPD among a plurality of parameters and transmits . At this time, since the stereo signal itself is not coded and transmitted, deterioration of sound quality may occur during reproduction of the stereo signal. Therefore, by adding a CLD offset or modifying the OPD value in the OPD calculation, a mono signal can be generated, thereby reducing the amount of bits and eliminating the phase discontinuity and minimizing deterioration of sound quality.

9 is a flowchart illustrating a method of decoding a multi-channel signal according to another embodiment of the present invention. The method of decoding a multi-channel signal according to the present embodiment may be performed by the apparatus 300 for decoding a multi-channel signal according to another embodiment of the present invention described above. 9, a description will be given of a method of decoding a multi-channel signal by explaining a process in which each step is performed by the multi-channel signal decoding apparatus 300. FIG.

In step 910, the multi-channel signal decoding apparatus 300 modifies parameters related to a phase difference between a mono signal and a multi-channel signal, which are downmix signals of the multi-channel signal. Here, the parameter related to the phase difference may include OPD estimated through a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting the multi-channel signal. In this case, the plurality of parameters may include channel level differences (CLD) between a plurality of channels, and the decoding apparatus 300 of the multi-channel signal may add a CLD offset to the value of CLD, Can be modified.

In addition, the multi-channel signal may include a plurality of frames, and the parameter modifier 350 may determine that the difference between the estimated OPD value of the frame one frame before the current frame and the estimated OPD value of the current frame is greater than or equal to the predetermined value , The estimated OPD value of the current frame can be modified. For example, the predetermined value may include 90 [deg.]. In this case, the multi-channel signal decoding apparatus 300 estimates the OPD value of the frame one frame before the current frame and the estimated OPD value of the current frame Is 90 DEG or more, the OPD value of the current frame can be modified by 180 DEG.

The method of adding the CLD offset or modifying the OPD through the difference of the OPD values between adjacent frames has been described above, and a duplicate description will be omitted.

The multi-channel signal decoding apparatus 300 up-mixes the mono signal using parameters related to the modified phase difference. That is, the multi-channel signal decoding apparatus 300 can up-mix the mono signal using the modified OPD to eliminate the phase discontinuity, thereby minimizing deterioration of the sound quality. Since the method of upmixing the mono signal has already been described in detail, repetitive description will be omitted.

In this case, the multi-channel signal may be received as an encoded bit stream from the multi-channel signal encoding apparatus 100 according to another embodiment of the present invention described with reference to FIG. 1, (300) can recover a mono signal and a plurality of parameters in this bit stream. At this time, as described above, the parameter OPD related to the phase difference can be estimated through a plurality of parameters. In order to obtain the mono signal from the bitstream and estimate the OPD, the apparatus 300 for decoding the multi-channel signal reconstructs the mono signal from the encoded bitstream of the multi-channel signal (not shown) A step (not shown) of restoring a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting the channel signal and a step of estimating an overall phase difference (OPD) as a parameter relating to a phase difference using the restored plurality of parameters Time).

As described above, according to the embodiments of the present invention, it is possible to reduce the amount of data required for data transmission and to provide a multi-channel audio signal with improved sound quality.

In addition, embodiments of the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded on a computer readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and configured for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Examples of program instructions, such as magneto-optical and ROM, RAM, flash memory and the like, can be executed by a computer using an interpreter or the like, as well as machine code, Includes a high-level language code. The hardware devices described above may be configured to operate as one or more software modules to perform operations of one embodiment of the present invention, and vice versa.

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and specific embodiments and drawings. However, it should be understood that the present invention is not limited to the above- And various modifications and changes may be made thereto by those skilled in the art to which the present invention pertains. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

300: Decryption device
340: up mixer
350: parameter modifier

Claims (7)

Restoring a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting a stereo signal;
Estimating an overall phase difference (OPD), which is a parameter related to a phase difference between one of a left channel signal and a right channel signal and a mono signal as a downmix signal of the stereo signal, using the restored plurality of parameters; And
Upmixing the mono signal using the recovered plurality of parameters and the estimated OPD,
The plurality of parameters including CLD and IPD,
Wherein estimating the OPD comprises:
And estimating the OPD to be 0 if the IPD is 180 and the CLD is zero. The method according to claim 1,
Further comprising restoring the mono signal from an encoded bit stream of the stereo signal,
Wherein the step of restoring the plurality of parameters comprises:
And reconstructing a plurality of parameters indicating a characteristic relationship between a plurality of channels constituting the stereo signal from the bitstream. delete delete The method according to claim 1,
Wherein estimating the OPD comprises:
Modifying the estimated OPD using the CLD and the IPD if the IPD is not 180 [deg.],
Wherein the modified OPD corresponds to one of a value between the estimated OPD and 0 [deg.] Or a value between the estimated OPD and -180 [deg.]. The method according to claim 1,
Wherein estimating the OPD comprises:
And modifying the estimated OPD so that the estimated amount of change of the OPD is reduced by filtering the estimated OPD. The method according to claim 6,
Wherein the modifying the estimated OPD comprises:
And filtering the estimated OPD using an Infinite Impulse Response (IIR).

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